If the restart designated by name is not invoked while executing forms, all values returned by the last of forms are returned. If the restart designated by name is invoked, control is transferred to with-simple-restart, which returns two values, nil and t.

Because the second return value is t in the exceptional case, it is common (but not required) to arrange for the second return value in the normal case to be missing or nil so that the two situations can be distinguished.